In automotive engine control, the amount of fuel to be injected is often determined either by measuring the engine speed and the mass air flow (MAF) into the intake manifold, known as the air meter method, or by inferring the air flow from the measurement of engine speed and manifold-absolute pressure (MAP), known as the speed-density method. For both approaches, during engine transient operations, the differences between the measured MAF, throttle position, or MAP and their past values are used to adjust the amount of fuel for the air flow changes. As the exhaust emissions standards become more stringent, more effective ways of engine fuel control are needed.
In the speed-density approach, as shown in FIG. 1, the measured MAP signal is filtered before it is used for air flow estimation. The result is then used to compute the amount of fuel needed, taking into account the effects of exhaust gas recirculation (EGR). During transient operations, additional calculations are needed to compensate for the transient air and fuel dynamics. These transient control routines are commonly known as acceleration enrichment (AE) and deceleration enleanment (DE). In particular, measured changes in MAP and throttle position (TPS) are multiplied by AE/DE gains and added to the base fuel calculation. They are used to account for errors from both air estimation and fuel dynamics estimation. That is, the changes in throttle position (or MAP) are directly used to calculate the transient fuel requirement.
Due to the differences in the nature of the air and fuel dynamics, the prior acceleration enrichment and deceleration enleanment approaches do not completely reduce the transient air-fuel ratio errors. It is well recognized that the change in throttle position, together with other variables, such as idle air actuator (IAC) and EGR, causes change in MAP, which in turn changes the amount of air drawn into the cylinders. The fuel dynamics, on the other hand, is strongly influenced by the air flow and the surrounding temperature conditions. Lumping these two significantly different dynamics makes accurate control of air-fuel ratio extremely difficult.